(a) Field of the Invention
The present invention relates to a microphone and more particularly, to a microphone that improves sensitivity without adding a separate circuit.
(b) Description of the Related Art
In general, a microphone is a device that converts audio to an electrical signal. A microphone should improve electromagnetic and audio performance, reliability, and operability. Additionally, a microphone is gradually formed to have a reduced size. Accordingly, a microphone using Micro Electro Mechanical System (MEMS) technology has been developed.
The MEMS microphone has a tolerance against moisture and heat, compared with a conventional Electret Condenser Microphone (ECM), and can be reduced in size and be integrated into a signal processing circuit. In general, a MEMS microphone may be classified into a piezoelectric MEMS microphone and a capacitive MEMS microphone.
The piezoelectric MEMS microphone is formed with a vibration film, and when the vibration film is changed by external audio, an electrical signal occurs due to a piezoelectric effect and thus a sound pressure is measured. The capacitive MEMS microphone includes a fixed electrode and a vibration film, and when audio is applied from the exterior to the vibration film, while a gap between the fixed electrode and the vibration film is changed, a capacitance value is changed. A sound pressure is measured based on an electrical signal occurring during the process.
However, because a vibration displacement of a film is limited, the method of increased sensitivity is limited. Accordingly, a method of increasing strength by simultaneously outputting and adding a signal of another form is introduced. For example, in conventional methods, a signal processing circuit is required for each of two output signals, when an additional circuit that adds signals is required. Accordingly, a semiconductor chip area increases resulting in price increases and a power consumption increase.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.